Among conventional RF-to-IF (radio frequency-to-intermediate frequency) mixers, zero-IF implementations have the inherent problem of LO (local oscillator) leakage through the mixer to the RF input, which then gets downconverted inside the mixer. One solution currently in discussion to solve this problem is to use a sub-harmonic pumped mixer for the down conversion. Such a mixer either requires very high LO drive currents or suffers from undesirably high noise figures. The sub-harmonic pumped mixer also generates the needed RF frequency internally, so there is still a LO leakage problem with this architecture. For low IF implementations, the realization of 90 degree phase splitters is one of the biggest challenges.
It is therefore desirable to provide a mixer that avoids the aforementioned disadvantages of conventional approaches.